Acquisition and properties of wear-resistant PVD/CVD coatings on a hard-alloy tool

Chapter 12 - Study of Two-Dimensional Phases on Electrodes

Processes of formation of intermetallic phases in functional coatings deposited by cold gas-dynamic sputtering of Ni - Al, Ni - Ti - Al, Ti - Al and Ni - Ti powder mixtures are studied. In heating of the coatings containing Al, the main phase transformations occur in the range of 450 - 750 °C; the processes of phase formation in the coatings based on the Ni - Al and Ni - Ti - Al systems develop in a similar manner. In the Ni - Ti coatings, transformations do not develop in the temperature range studied. The phase transformations in the coatings are identified.

The results of given studies included a comparison of changes in temperature, redox potential, OH‐ions concentration and pH values in the Portland cement‐water‐additive system depending on the hydration time and features of hydration processes in the microstructure of the cement stone. The studied additives were selected taking into account the prospects for their use in the complex modifiers compositions for cement‐containing building materials. The results of electrokinetic measurements are presented and regularities and features of the influence of each studied additives on the processes of hydration structure and phase formation in Portland cement paste in the early stages of hardening are determined. The microstructure and fracture surfaces of cement stone samples formed during cement paste hardening with the optimal content of additives and features of hydration processes of cement stone were studied. The features of the mutual arrangement of individual phases in crystalline hydrate aggregates of cement stone, as well as the nature of the porosity of its microstructure, were investigated.

Mathematical and experimental modelling of quenching a self-propagating high-temperature synthesis process

Unveiling the role of Cs ion in perovskite phase formation during solid–vapor reactions

ABSTRACTTwenty years of research have now been devoted to investigating reaction products obtained by annealing metal-layer/silicon structures. A wide variety of cases have been analyzsed and a considerable amount of data has been produced. Despite the vast amount of information available, several aspects concerning phase formation and kinetic processes are not yet well established. The purpose of this paper is to investigate the mechanisms of phase formation and to show the importance of kinetic factors in the appearance of various compounds. Results will be shown for a single metal layer deposited on silicon, for bilayers. and for alloys. Depending upon the starting structure, metal-rich or silicon-rich silicides can be formed. Moreover, by modifying the boundary conditions, it is possible to change the growth kinetics of the silicide phase that forms.

We systematically investigate the internal friction properties of a Fe–(43 at.%)Al powder mixture compact during the heating process with the expectation to understand the phase formation and transition process. Three internal friction peaks are successively observed during the heating process from room temperature to 750°C, but almost completely disappear in the subsequent cooling process. Three internal friction peaks exhibit obvious measuring frequency dependence, which increases with decreasing the frequency. The first internal friction peak originates from the micro-sliding of weak bonding interface between Al particles corresponding to a recrystallization process of deformed Al particles. The second internal friction peak is attributed to a phase formation process associated with the formation of the intermediate phase Fe2Al5. The third internal friction peak is considered to result from the formation of the FeAl intermetallic compound owing to the reaction of Fe2Al5 and residual Fe initiated by a dramatic thermal explosion reaction.

Chapter 1 - Ferroelectric Thin Films: Preparation and Characterization

In the present paper, some further results of application of the generalized Gibbs' approach to describing new-phase formation processes are outlined. The path of cluster evolution in size and composition space is determined taking into account both thermodynamic and kinetic factors. The basic features of these paths of evolution are discussed in detail for a simple model of a binary mixture. According to this analysis, size and composition of the clusters of the newly evolving phase change in an unexpected way which is qualitatively different as compared to the classical picture of nucleation-growth processes. As shown, nucleation (i.e., the first stage of cluster formation starting from metastable initial states) exhibits properties resembling spinodal decomposition (the size remains nearly constant while the composition changes) although the presence of an activation barrier distinguishes the nucleation process from true spinodal decomposition. In addition, it is shown that phase formation both in metastable and unstable initial states near the classical spinodal may proceed via a passage of a ridge of the thermodynamic potential with a finite work of the activation barrier even though (for unstable initial states) the value of the work of critical cluster formation (corresponding to the saddle point of the thermodynamic potential) is zero. This way, it turns out that nucleation concepts-in a modified form as compared with the classical picture-may govern also phase formation processes starting from unstable initial states. In contrast to the classical Gibbs' approach, the generalized Gibbs' method provides a description of phase changes both in binodal and spinodal regions of the phase diagram and confirms the point of view assuming a continuity of the basic features of the phase transformation kinetics in the vicinity of the classical spinodal curve.

This article examines the processes of structure formation occurring during joint plastic deformation by the explosion of copper and molybdenum. These components are dissimilar metals with very limited mutual solubility under normal conditions, and the circumstances allowing for their interaction, as well as the products of the mechanochemical reactions of such interactions, have not been sufficiently studied and require new approaches. A cluster approach was used to describe the processes of structure formation, which describes phase formation as the process transitioning of the polyhedron of the initial phase into the polyhedron of the final phase. This work shows that under the conditions under consideration, not only is the formation of solid solutions in the contact zone with smooth concentration transitions from one component to another possible, but also the formation of new structural states, which can be represented as localized icosahedral atomic configurations (amorphous metal clusters). Such a structure is capable of locally strengthening the composite, which is confirmed by microhardness studies.

The subject of the research is features of synthesis of alumina cements on the basis of compositions of system CaO – CoO – Al2O3 – MoO3 with use of cobalt‐molybdenum‐containing waste for reception of refractory materials with a complex of the set properties. The processes of phase formation in raw mixtures have been investigated. X‐ray phase studies of clinkers fired at different temperatures and holding times proved that as a result of the interaction of the raw materials of the mixture in the material synthesizes a mixture of hydraulically active calcium mono‐ and di‐aluminate and refractory cobalt spinel, which provides the resulting complex high strength, accelerated curing time, fire resistance. The absence of phases corresponding to molybdenum compounds is explained by the fact that they are part of hydraulically active aluminates as limited solid solutions, deforming the crystal lattice and increasing hydraulic activity. Thus, it was found that the high strength of cement is due to the presence of calcium hydroaluminates such as C2AH8, aluminum hydroxide, as well as unhydrated grains of calcium aluminates, which will contribute to further long‐term strength. It is this coexistence of phases in both the crystalline and colloidal states provide high strength cement stone.

The thermodynamic and ab initio molecular dynamic approaches have been applied to analyze the phase formation processes in amorphous alloys of Fe–Zr system. The thermodynamic calculations of the kinetics of the phase formation process of binary amorphous alloys of the Fe–Zr system with continuous slow heating and pulsed laser processing are carried out. It was shown that the processes of phase formation in the binary alloys of the Fe–Zr system take place in two stages: initially, there are processes of phase stratification on two amorphous phases according to the type of spinodal decomposition, then crystallization of each amorphous phase. The calculations carried out within the framework of the modified theory of homogeneous nucleation for binary systems have shown that the process of crystallization of binary alloys of the Fe–Zr system with continuous slow heating is two-step: first, the solid solution Zr in α-Fe crystallizes, then the chemical compound Fe3Zr, with complete crystallization occurs in the temperature interval of 90 K. It was shown that the region of amorphization of binary alloys of the Fe–Zr system is within (3–15)% at. zirconium, which is well in agreement with experimental data. The theoretical confirmation of the possibility of a course of explosive crystallization during pulsed laser annealing in binary amorphous alloys of the Fe–Zr system at a temperature lower than 60 K for the temperature of the beginning of intensive crystallization at slow heating. First-principles molecular dynamics simulations of amorphization and crystallization process in the Fe–Zr system have been presented. The atomic positions in the Fe29Zr3 supercell were modeled by simulating annealing by the density functional theory in the generalized gradient approximation. Changes in the density of electronic states of the Fe29Zr3 supercell under liquid-amorphous-crystalline phase transitions are discussed. The most marked difference between the electronic spectrum of liquid and amorphous phases is a pseudogap at the Fermi level which is consistent with the Nagel–Tauc electronic criterion of the amorphous metallic alloy thermal stability. Further simulating annealing in the isothermal/isenthalpic ensemble under the higher temperatures leads to the drastical changes of the electronic spectrum and rearrangement of atoms, which we assign to the first stage of the amorphous alloy crystallization.KeywordsAmorphous alloyRelative integral free gibbs’ energyVolume part of crystalline phaseCrystallization processExplosive crystallizationPulsed laser annealingElectronic structureAb initio molecule dynamic

Advanced large-scale integrated interconnect structure faces a major challenge in forming a thin and conformal diffusion barrier layer. We deposited a Mn oxide layer by thermal chemical vapor deposition (CVD) on SiO2 substrates and investigated deposition behavior and diffusion barrier property. A thin Mn oxide layer was formed with a uniform thickness of 2.6–10nm depending on deposition temperature between 100 and 400°C. Heat-treated samples of Cu/CVD-Mn oxide/SiO2 indicated no interdiffusion at 400°C for 100h. The CVD of the Mn oxide layer was found to be an excellent barrier formation process.

The potential use of germanide thin films as self‐aligned metallization in Ge‐based Complementary Metal‐Oxide Semiconductor (CMOS) technology has drawn interest in the solid‐state reactions of Ge and metal films [1‐3]. In order to integrate these germanide thin films as a contact material, a complete analysis of the solid‐state reactions of amorphous Ge (a‐Ge) and metals is required. The solid‐state reactions in the Co‐Ge thin films systems previously examined by in situ x‐ray diffracting annealing experiments only probed the crystal structures present in the film and did not identify the morphological variations of the process [1]. Furthermore, to the authors knowledge previous works Co‐Ge thin film systems have only analyzed systems with Ge in excess of Co. In this study, the phase formation and crystallization behavior of a‐Ge and Co thin film layers are investigated by ex situ transmission electron microscopy (TEM) coupled with in situ x‐ray diffraction (XRD) annealing experiments. Four different specimens were prepared, alternating the stacking order and film thickness (200 nm and 30 nm), in order to explore the influence of the free surface on the crystallization and the phase reactions with Co in excess of a‐Ge. Thin film layers of a‐Ge and Co were deposited via electron beam evaporation onto (100) silicon wafers with the native oxide film present on the surface (~1–2 nm). The thin film specimens were characterized by TEM before and after annealing during the phase formation process. Bright field TEM images of the 200 nm Co on top of 30 nm a‐Ge stack are shown in Figure 1: (a) as‐deposited, (b) annealed at 280°C and (c) 400°C. Upon heating to 280°C, the a‐Ge layer reacts with the Co layer to form CoGe, which then undergoes an additional phase transformation to CoGe 2 with continued heating to 400°C. The influence of the free surface ( fs ) on the crystallization process was examined on the 200 nm a‐Ge and 30 nm Co film stack. The scanning electron microscopy images of the specimens after annealing to 400°C are shown in Figure 2. (a) The specimen with a‐Ge at the free surface (a‐Ge fs ) shows two distinct contrast indicating the presence of two different crystalline phases near the surface, while (b) the specimen with Co at the free surface (Co fs ) shows a more homogeneous contrast throughout the surface. Both specimens have voids visible at the surface, which formed during annealing. By viewing the specimens in cross‐section, the presence of large voids is visible in (c) the specimen a‐Ge fs , but the voids are not present in (d) the specimen with Co fs . The resulting formation of voids in only one of two specimens indicates the free surface has a direct influence of the phase formation process.

The processes of structure formation in the final stage of production of die-rolled-section hardware from steel 20SG are considered. It is shown that the kinetics of the variation of the structure and properties of steel 20SG depending on the time of the post-deformation hold corresponds to the processes of recrystallization after the hot deformation. The processes of structure formation reflect the actual situation in the commercial production of the hardware.